Method for reacting self-igniting dusts in a vacuum pump device

ABSTRACT

Into a vacuum pump device arranged for suctional intake of a process gas ( 38 ) possibly comprising reactive particles ( 40 ), oxygen in the form of air or pure oxygen is supplied in a controlled manner via an oxygen intake ( 26, 26   a,   26   b ). Thus, controlled oxidation takes place in the compression chamber ( 24 ) such that the dust cannot self-ignite in case of sudden ventilation.

BACKGROUND

The invention relates to a method for exhaustive reaction of self-igniting dust in a dry-sealed vacuum pump device, as well as a corresponding vacuum pump.

In metallurgical and various other processes performed in a vacuum environment, it is frequently the case that particles or fine dust are generated, which due to their chemical composition and their large surface are so reactive that they will self-ignite upon contact with ambient air, thus entering an exhaustive reaction with the aerial oxygen. Examples of such processes are the Czochralsky method for producing silicon monocrystals, or the melting and degassing of steels. In the first case, silicon oxide (SiO) is generated, and in the second case, metallic fine dust such as e.g. magnesium dust, are generated. The dust particles are sucked into the vacuum pump which generates the vacuum required for the process. In oil-sealed vacuum pumps, the dust particles are absorbed by the lubricant and will not be discharged from the pump. Since the particles are mostly very hard and together with the oil will act like a grinding agent, this will often lead to massive wear within the vacuum pump. In dry-sealed vacuum pumps, on the other hand, such as e.g. screw-type vacuum pumps, the massive reaction upon sudden contact with oxygen involves a danger of explosions. Therefore, in both cases, the assemblies are provided with complex dust filters which will filter out the dust upstream of the vacuum pump. The dust will accumulate within the dust filter, whereby, however, the danger of explosion is not eliminated. In dry-sealed pumps, there is also a possibility of dust accumulating on the exhaust side of the vacuum pump.

The dust also causes a safety hazard to the maintenance personnel of the systems because, in case of faulty operating or unintentional venting of the system, inflammation of the dust cannot be excluded. Such an inflammation may even occur in the filter or in the tubing.

It is an object to provide a method for exhaustive reaction of self-igniting dust in a dry-sealed vacuum pump, which method shall effect a continuous oxidation of the reactive dust within the vacuum pump, so that the vacuum pump per se is simplified and the working processes to be performed at the vacuum pump are made safer.

During operation of the vacuum pump device, oxygen is continuously supplied thereto in a dosed manner, whereby an oxidation of the dust is effected.

SUMMARY

One aspect provides a well-aimed exhaustive reaction of oxidizable dust in the vacuum pump. Thus, for instance, silicon oxide (SiO) is oxidized to silicon dioxide (SiO₂), and metals are oxidized to metal oxides. Since it is substantially gas that is conveyed by the vacuum pump and since the absolute mass flow of dust per time unit is relatively small, the present method offers the possibility to accomplish a continuous and controlled exhaustive reaction of the reactive dust. Uncontrolled inflammation of the dust is reliably prevented. The supplying of oxygen can be provided in the form of pure oxygen or in the form of air. The oxygen supply will affect the suction performance of the pump only to a mere negligible extent. The dust quantity introduced into the vacuum pump per time unit is small enough to be continuously burned with a relatively low air-gas ballast while this burning process will not cause damage to the pump. All of the particles leaving the pump again on the pressure side will have undergone an exhaustive reaction. Consequently, a separation of dust can be performed by use of normal dust filters on the pressure side without a danger of uncontrolled reactions. This allows for a simplified and less expensive installation of the vacuum pump. Possible accumulations of dust in the tubing on the exhaust side will not be reactive anymore and thus will be of no concern under the aspect of safety technology.

The supplied oxygen-containing gas can be fed into the vacuum pump device at a suitable site, e.g. into the pumping chamber at the entrance to the pump, at a site along the compression chamber, or at the pump exit.

Another aspect relates to a dry-sealed vacuum pump device comprising at least one driven compression member and a housing with pump entrance and pump exit. The vacuum pump is characterized in that the housing comprises at least one oxygen entrance provided with a throttle valve for regulating the cross section of the entrance.

Possible embodiments of a dry-sealed vacuum pump are the following: screw pumps, claw-type pumps, Roots pumps, turbo compressors, lateral-channel blowers, dry-sealed rotary-vane pumps, and others.

The vacuum pump device can comprise a sole vacuum pump, or a plurality of pumps connected in series and each forming a pump stage. The oxygen can also be introduced into a reaction chamber arranged between two pump stages. As a reaction chamber, use can be made also of a tube conduit.

According to a modified embodiment, temperature and pressure sensors are provided for monitoring the reaction in the vacuum pump device.

A method for cleansing the vacuum pump device and the feed conduits from dust can reside in that, after the end of the process, the supply of process gas is terminated while the supply of an oxygen-containing gas mixture, e.g. air, through the pump device is continued.

Finally, the oxygen required for oxidation can also be contained in the buffer gas of a shaft sealing. In this case, the oxygen will flow in dosed quantities from the shaft sealing into a pump chamber or into a conduit of the pump device.

The following is a detailed description of an embodiment of the invention with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal sectional view through the compression chamber of a vacuum pump,

FIG. 2 is a sectional view taken along line II-II in FIG. 1, and

FIG. 3 is a schematic representation for illustrating the principle of the present invention.

DETAILED DESCRIPTION

According to FIG. 1, there is provided a vacuum pump in the form of a screw pump. Said pump comprises an elongate housing 10 supporting therein two screw rotors 12,14 for rotation in opposite senses. Each screw rotor comprises a helically configured tooth 16,18 with a pitch continuously decreasing from the pump entrance 20 to the pump exit 22, as can be seen in FIG. 1. Thereby, the working chamber, which in rotating rotors will be traveling in axial direction, is reduced in size from pump entrance 20 towards pump exit 22. Between the pump entrance and the pump exit, the compression chamber 24 is arranged.

Pump entrance 20 forms the pumping chamber which will be connected to the device that is to be evacuated. Into this pumping chamber, the process gas 38 will be sucked. The process gas contains particles 40 in the form of non-oxidized dust.

Pump entrance 20 is connected to an oxygen intake 26 which is laterally arranged on housing 10 and is provided with a throttle valve 28. Throttle valve 28 can be set to various throttle cross sections so as to regulate the oxygen supply. The oxygen can be pure oxygen or a component of a gas mixture, e.g. of air.

Within pump housing 10, the dust will undergo a controlled reaction with the supplied oxygen as soon as, during condensation, an oxygen partial pressure as required for reaction has been reached.

An alternative embodiment of the oxygen intake is designated by 26 a. Oxygen intake 26 a is located in the region of the mid-length of compression chamber 24, namely in the middle between the two mutually engaging helically shaped teeth 16,18.

A third alternative includes the oxygen intake 26 b arranged on pump exit 22.

At each of said oxygen intakes 26,26 a, due to the vacuum prevailing there, the oxygen and respectively the ambient air will be sucked in. The above oxygen intake 26 b, however, is located at the pump exit 22 where atmospheric pressure prevails. For this reason, a connected oxygen source must be subjected to overpressure. In any case, a throttle valve 28 is provided on the oxygen intake.

FIG. 3 is a schematic representation of the pump with the pump entrance 20 for suctional intake of the process gas 38. In this Figure, oxygen intake 26 is arranged at the suction connector of pump entrance 20.

In FIG. 3, the black sphere symbols represent the non-oxidized particles, and the hollow sphere symbols represent the oxidized particles. Oxidation takes place in compression chamber 24 in dependence on which intake among the oxygen intakes 26,26 a,26 b is in the opened state.

In FIG. 3, the shafts for rotating the screw rotors are designated by 30.

The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

1. A method for exhaustive reaction of self-igniting dust in a dry-sealed vacuum pump device, comprising: during operation of the vacuum pump device, continuously supplying oxygen thereto in a dosed manner, whereby an oxidation of the dust is effected.
 2. The method according to claim 1, wherein said supplying of oxygen takes place at at least one of an entrance of the vacuum pump device and in the feed lines of the vacuum pump device.
 3. The method according to claim 1, wherein said supplying of oxygen takes place along a compression chamber of the vacuum pump device.
 4. The method according to claim 1, wherein said supplying of oxygen takes place along or between at least two compression chambers.
 5. The method according to claim 1, wherein the supplying of oxygen is performed at an exit or in exhaust lines of the vacuum pump device.
 6. The method according to claim 1, wherein the supplying of oxygen is performed via a settable or controllable throttle valve.
 7. The method according to claim 1, further including: terminating supplying a process gas for condensation, and continuing the supplying of an oxygen-containing gas mixture, for cleaning the pump device and the supply lines from dust and for exhaustive reaction of the dust.
 8. A dry-sealed vacuum pump device comprising: at least one driven compression member; and a housing with a pump entrance and a pump exit, one of said housing or a line connected thereto comprises at least one gas and respectively oxygen intake provided with a throttle valve for regulating an entrance cross-section.
 9. The vacuum pump device of claim 8, further including: at least one of temperature sensors and pressure sensors in a chamber in which dust is oxidized to monitor a dust oxidation reaction.
 10. A method of reacting exhaust dust in a dry-sealed vacuum device, comprising: with a dry-sealed vacuum device, sucking in a process gas with flammable dust; introducing oxygen into the exhaust gas in or adjacent the dry-sealed vacuum device; compressing the process gas with flammable dust and the oxygen in a compression chamber of the dry-sealed vacuum device; oxidizing the flammable dust with the introduced oxygen in the dry-sealed vacuum device; and discharging the process gas and oxidized dust. 